I am guessing WPG isn't a good measure because of the widely varying types of light or..............?
Yes, as the efficiency or the lamps and ballasts has inceased and the differences in types of lighting and bulb configuration....the WPG
(started for FW
planted tanks using NO
lamps) has gone down the toilet. First watts is a measure of electrical consumption, not light output. If all lamps were created equal that still might be ok...but they are not. In the above reference, to measure MH
on a tank longer than 2ft (the effective range of the halide) you have to split it in half, and it still isn't very good.